The present invention relates to the correction of spinal deformities. Specifically, it relates to moving a vertebra to a desired relationship with other vertebrae and maintaining the desired relationship.
Devices for correcting spinal column deformities are known. U.S. Pat. No. 3,997,138 discloses a device which has a pair of flexible rods or cables to maintain adjacent vertebrae in a desired relationship. The rods or cables are secured to fasteners connected with the vertebrae.
Devices which include rigid plates are also known for securing vertebrae in a desired relationship. The plates are relatively heavy. Each plate has longitudinal slots formed therein which do not permit flexibility in locating fasteners laterally in the vertebrae.
Another known device for correcting spinal deformities is a ratchet system. The ratchet system includes a rod and ratchet blocks which engage the rod. The rod spans several vertebrae. The ratchet blocks have hooks. The hooks grab around pedicles on the vertebrae. The hooks are then drawn together by the rod to apply a desired correction to the spinal column. The ratchet system can only compress the spinal column.
In another device, the corrective forces are applied by two steel rods which are wired around the spine. The rods are not directly attached to all the vertebrae that the rods span. Maintaining a desired spatial relationship among the vertebrae spanned by the rods is difficult.
Another known spinal corrective device is disclosed in U.S. Pat. No. 4,041,939. The device includes fasteners which are threaded into the vertebrae. A cable is threaded through openings in the head of each fastener. Tension is applied to the cable to move the vertebrae to a desired relationship. The fasteners are crimped around the cable to maintain the desired relationship. This device can only compress the spinal column. Once the cable is crimped into place, no further adjustment is possible.